The present invention is directed to aircraft flight control systems and, in particular, to reducing the occurrence of transient behavior at a control interface or an aircraft while transitioning between operating modes of the aircraft.
Fly-by wire (FBW) control systems are increasingly employed in the control of rotary-wing aircraft. Such FBW systems allow the aircraft to operate in one or more operational modes. In a ground control proportional mode, a pilot moves a control device, such as a cyclic, collective or pedals, and an aircraft flight control surface such as a swashplate or servo moves in direct proportion to the movement of the control device. In a model following controls operational mode, a movement of the control device indicates a desired response of the aircraft. The desired response is interpreted by a control system which determines a configuration of the flight control surface that produces the desired response. When transitioning from the ground control proportional mode to the model-following controls mode, a trim condition of the aircraft is taken from the control device (i.e., the cyclic) and is faded into a trim integrator of the control system. This transition usually introduces a transient into the aircraft as a result of the proportional cyclic offset being faded into the trim.
Accordingly, it is desired to provide a transition between operational modes of the aircraft without the occurrence of transients at the control device.